I've heard of collecting water with tarps and assume this is like a vest form of that:

https://www.campingsurvival.com/blogs/camping-survival-blogs...

Collecting water with tarps is just strategic collection of condensation/dew. Clothing has the issue of often being warmer than ambient because people are warm blooded, so it's unlikely water would condense from the air(though it can condense on the inside from evaporated sweat).